1. Field of the Invention
This invention relates to video processing and particularly to motion compensation techniques.
2. Background Art
The use of motion compensation is well known in a variety of processes, of which standards conversion is a good example. In one prior art approach, each output field is constructed from a number of stored input fields. For a given output pixel, information is read from the pixels in the input fields in conjunction with the motion vector associated with the required pixel. A problem associated with this approach is that the motion vectors must first have been converted to the new standard, causing extra complexity and creating artefacts.
A different approach to motion compensated standards conversion is detailed in EP 0 648 398. Here, the motion vectors are employed in writing the input fields to a store and the output picture is constructed as data is accumulated in the store. This method of approach has a number of advantages, including use of motion vectors at the input standard. There can sometimes be a difficulty, however, with discontinuous motion.
When there is discontinuous motion in the video source to be converted, the motion vectors from the outer of the four input fields may, when extrapolated to the output field position, point to different positions for the output pixel, creating aliasing and multiple images.
It is hence an object of the present invention to provide a motion compensated standards conversion system that results in a sharp output even in the face of discontinuous motion.